There are a number of oxidizing compounds that are satisfactory for disinfecting water systems. It would be desirable to be able to incorporate a blue pigment in these compounds so that they could be identified as a disinfectant. It would be necessary for the pigment to be stable when incorporated in dry form with the compound. As these oxidizer compounds are used for disinfecting other systems such as swimming pools and spas, it is preferred that the pigment not be stable in the water system. Otherwise it might stain the walls of the swimming pool and spa even though it is used in very small amounts.